The present invention relates to organic semiconductors and to the use thereof in organic electronic devices.
Organic semiconductors are being developed for a number of electronic applications of different types. The structure of organic electroluminescent devices (OLEDs) in which these organic semiconductors are employed as function al materials is described, for example, in U.S. Pat. No. 4,539,507, U.S. Pat. No. 5,151,629, EP 0676461 and WO 98/27136. However, further improvements are still necessary before these devices can be used for high-quality and long-lived displays. Thus, in particular, the inadequate lifetime and the inadequate efficiency of blue-emitting organic electroluminescent devices currently still represent a problem which has not yet been satisfactorily solved. Furthermore, it is necessary for the compounds to have high thermal stability and a high glass-transition temperature and to be sublimable without decomposition. In particular for use at elevated temperature, a high glass-transition temperature is essential in order to achieve long lifetimes.
For fluorescent OLEDs, principally condensed aromatic compounds, in particular anthracene derivatives, are used in accordance with the prior art as host materials, especially for blue-emitting electroluminescent devices, for example 9, 10-bis(2-naphthyl)anthracene (U.S. Pat. No. 5,935,721). WO 03/095445 and CN 1362464 disclose 9,10-bis(1-naphthyl)anthracene derivatives for use in OLEDs. Further anthracene derivatives are disclosed in WO 01/076323, in WO 01/021729, in WO 04/013073, in WO 04/018588, in WO 03/087023 or in WO 04/018587. Host materials based on aryl-substituted pyrenes and chrysenes are disclosed in WO 04/016575. For high-quality applications, it is necessary to have improved host materials available.
Prior art which may be mentioned in the case of blue-emitting compounds is the use of arylvinylamines (for example WO 04/013073, WO 04/016575, WO 04/018587). However, these compounds are thermally unstable and cannot be evaporated without decomposition, which requires high technical complexity for OLED production and thus represents a technical disadvantage. It is therefore necessary for high-quality applications to have improved emitters available, particularly with respect to device and sublimation stability and emission colour.
There thus continues to be a demand for improved materials, in particular host materials for fluorescent emitters, especially for blue-fluorescent emitters, and fluorescent materials which are thermally stable, result in good efficiencies and at the same time in long lifetimes in organic electronic devices, give reproducible results during the production and operation of the device and are readily accessible synthetically. Further improvements are also necessary in the case of hole- and electron-transport materials.
Surprisingly, it has been found that benz[a]anthracene derivatives which are substituted in at least one of positions 2, 3, 4, 5 or 6 by an aromatic or heteroaromatic group, by a diarylamino group or by one of the other groups defined below are very highly suitable for use in organic electroluminescent devices. These compounds enable an increase in the efficiency and especially the lifetime of the organic electronic device compared with materials in accordance with the prior art. This applies, in particular, to blue-fluorescent devices. Furthermore, these compounds have high thermal stability. In general, these materials are very highly suitable for use in organic electronic devices since they have a high glass-transition temperature. The present invention therefore relates to these materials and to the use thereof in organic electronic devices.
Benz[a]anthracene derivatives which are substituted in these positions by aromatic substituents have already been described sporadically in the literature (for example K. Maruyama et al., Chem. Lett. 1975, (1), 87-88; C. L. L. Chai et al., Austr, J. Chem. 1995, 48(3), 577-591, M. C. Kloetzel of al., J. Org. Chem. 1961, 26, 1748-1754 etc.). However, only the synthesis and reactivity of these compounds have been investigated. The use of these compounds in organic electronic devices has not been proposed. Furthermore, WO 05/090365 has disclosed a multiplicity of organosilane compounds containing polycyclic aromatic groups, inter alia also for use in organic electroluminescent devices, also including, besides numerous other compounds, a compound which is an aryl-substituted benzanthracene. The particular effect of these compounds is attributed here to the presence of the organosilyl group and not to the substituted benzanthracene skeleton.
For reasons of clarity, the structure and numbering of benz[a]anthracene are shown below:
